This invention relates to an apparatus and non-invasive method for ablating eye tissue using transclerally delivered electric currents. A specific application of this invention includes reduction of intraocular pressure by focal destruction of the ciliary process.
Glaucoma is a potentially debilitating disease of the eye in which the intraocular pressure within the eye rises above normal levels. Glaucoma is generally treated by a surgical procedure where a small hole is introduced through the sclera, i.e., the outer coating of the eye, to allow fluid within the eye to drain into the subconjunctival space, between the conjunctiva and the sclera.
Cycloablation, i.e., destruction of the ciliary body, is another method by which an opthamologist can reduce intraocular pressure. The ciliary processes are involved in the production of fluid within the eye. Thus, by destroying the ciliary processes, aqueous production is reduced. Cylcoablation is primarily prescribed for advanced glaucoma patients with poor vision.
At present there are a number of cycloablative or cyclodestructive procedures. These procedures include cyclocryotherapy, transscleral Nd:YAG laser cycloablation, therapeutic ultrasound, cyclodiathermy, and transpupillary argon ciliary process photoablation. Potential side-effects associated with these procedures include a post-treatment pressure spike, marked intraocular inflammation and unpredictability. The degree of unpredictability is such that in some cases phthisis bulbi ensues. A preferred technique would be one which is more predictable, and associated with minimal inflammation.
Iontophoresis, i.e., a means of introducing drugs in ionized form into tissues by passage of electric current, has become increasingly popular in North America over the past several years. Its applications range from dye-enhance ablation with laser sclerotomies to the experimental treatment of keratitis and endophthalmitis using antibiotics. Most research concerning the use of iontophoresis utilizes the method as a non-invasive mode of introducing effective levels of drugs to various regions of the eye, such as the vitreous humor. Using existing methods of drug administration, current, probe diameter and time parameters are regulated to avoid tissue damage. See, for example, U.S. Pat. No. 4,564,016 to Maurice et al.
One reference, Berens, Sheppard, and Duel, Cycloelectrolysis for Glaucoma, J. Trans. Am. Opthalmol Soc. 47:364-382 (1949), describes the use of electricity to destroy the ciliary body. The technique described involves invasive insertion of a needle directly through the sclera into the ciliary body. In a majority of cases, dissection of the conjunctiva was required and 50-75 punctures were recommended. While such invasive means did alleviate ocular pressure, complications such as infections may arise related to the procedure and the procedure never gained acceptance because of its invasive nature.
Thus, there remains a need for a non-invasive means for relieving intraocular pressure and an efficient, less traumatic means for selectively ablating eye tissue.